The field of spectroscopy general relates to the measurement of electromagnetic spectra, which may arise from emission or absorption of radiant energy. The field may also relate to an interpretation of the spectra based on common conventions. For example, the use of a spectrometer to analyze burning fuel can reveal the presence of potentially harmful by-products or whether the fuel meets the standards a customer or government has established.
Typically, usable emission spectra are produced when radiant energy from matter, excited by various forms of energy (in this case, light), is passed through a slit and then separated into its various components (wavelengths in the case of light analysis). This may be accomplished with either a semi-transparent prism (a refraction basis of analysis) or with a ruled grating (frequently a crystalline solid, a diffraction basis of analysis). Laser-based spectra analysis is a subset of this general field, where the production of a given wavelength of light is fixed to some known wavelength range and intensity and assigned a nominal expected variance inside of this fixed specification. The energy produced from this fixed source arrives at the spectrometer for analysis. The light may experience absorption or attenuation, from either the object of interest or background interference (from sources of no real interest to the investigators). Spectroscopic measurements of wavelengths and intensities of electromagnetic radiation are made using instruments called spectroscopes, spectrographs, spectrometers, or spectrophotometers.
The interpretation of spectra is more complicated, and chemists have found such an analysis tool to be of great value. In the past, communications companies have used variability in spectra to encode additional information in a single real path length. Normally used in a fiber-based connection across a building, the use of several lasers close in wavelength for increasing the bandwidth of a connection is one mechanism for increasing the bandwidth a system provides.
Conventional spectrometers have not gained wide use in the field of communications for two reasons—either the power consumption exceeds the power available, or the analysis time is unacceptable. Whether based on refraction or diffraction, spectrometers typically include a focusing lens with two optical surfaces, a slit, followed by at least three optical surfaces and frequently more than three optical surfaces. From an engineering standpoint, the additional elements used for traditional spectrometry result in an unacceptable loss of power. Several Fourier and inverse Fourier spectrometers have designs which dramatically reduce the number of elements. However, such spectrometers add analysis time where some applications demand results in real-time. Thus, additional time required to interpret the spectrum into meaningful information can be unacceptable.